146 PRACTICAL ORGANIC CHEMISTRYthe terminal group. It will be seen that a methyl aldopento-furanoside (I) willgive solely the dialdehyde (II), whereas a methyl aldohexo-pyranose (III) willgive the dialdehyde (IV) and one equivalent of formic acid, which may beestimated.In the following examples, pinacol is oxidised to acetone, which is identified asits semicarbazone and its 2,4-dinitrophenylhydrazone, and glycerol is oxidised toformaldehyde and formic acid. The formaldehyde is readily detected by the con-densation product which it gives with "dimedone," 5,5-dimethylcyclohexan-i,3-dione (p. 277).For these experiments, prepare two solutions: (A) A solution of2-5 g. of sodium metaperiodate in 50 mi. of water. A clear solutioncan be readily prepared by gentle warming, and then cooled.(B) A solution of i g. of "dimedone" (preparation, p. 277) in 10 ml.of ethanol. This solution will be required only for the glycerol oxida-tion experiment.
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